Homework 7 - [Map, Filter, Fold]

Functions/Functions.Tests/Functions.Tests.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net9.0</TargetFramework>
+    <LangVersion>latest</LangVersion>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+
+    <IsTestProject>true</IsTestProject>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="coverlet.collector" Version="6.0.2" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.12.0" />
+    <PackageReference Include="NUnit" Version="4.2.2" />
+    <PackageReference Include="NUnit.Analyzers" Version="4.4.0" />
+    <PackageReference Include="NUnit3TestAdapter" Version="4.6.0" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <Using Include="NUnit.Framework" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="../Functions/Functions.csproj"/>
+  </ItemGroup>
+
+</Project>

Functions/Functions.Tests/FunctionsTests.cs

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+// <copyright file="FunctionsTests.cs" company="Ilya Krivtsov">
+// Copyright (c) Ilya Krivtsov. All rights reserved.
+// </copyright>
+
+namespace Functions.Tests;
+
+public class FunctionsTests
+{
+    private static readonly IEnumerable<int> NumberSequence = Enumerable.Range(0, 120);
+
+    [Test]
+    public void Map_ConvertsNumbersToString_SameAs_Select()
+    {
+        AssertMapBehavesSameAsSelect(NumberSequence, x => x.ToString());
+    }
+
+    [Test]
+    public void Map_ConvertsStringToNumbers_SameAs_Select()
+    {
+        AssertMapBehavesSameAsSelect(NumberSequence.Select(x => x.ToString()), int.Parse);
+    }
+
+    [Test]
+    public void Filter_SelectsNumbers_SameAs_Where()
+    {
+        AssertFilerBehavesSameAsWhere(NumberSequence, x => x % 2 == 0);
+    }
+
+    [Test]
+    public void Filter_SelectsStrings_SameAs_Where()
+    {
+        AssertFilerBehavesSameAsWhere(NumberSequence.Select(x => x.ToString()), x => x.Contains('4'));
+    }
+
+    [Test]
+    public void Fold_SumsNumbers_SameAsAggregate()
+    {
+        static int Sum(int x, int y) => x + y;
+
+        var aggregateResult = NumberSequence.Aggregate(Sum);
+        var foldResult = NumberSequence.Fold(Sum);
+
+        Assert.That(aggregateResult, Is.EqualTo(foldResult));
+    }
+
+    [Test]
+    public void Fold_AddsCharacters_SameAsAggregate()
+    {
+        static string Sum(string x, char y) => x + y;
+
+        var source = Enumerable.Range('0', '~' - '0').Select(x => (char)x);
+
+        var aggregateResult = source.Aggregate(string.Empty, Sum);
+        var foldResult = source.Fold(string.Empty, Sum);
+
+        Assert.That(aggregateResult, Is.EqualTo(foldResult));
+    }
+
+    [Test]
+    public void Fold_AddsCharactersAndReverses_SameAsAggregate()
+    {
+        static string Sum(string x, char y) => x + y;
+        static string Reverse(string s) => string.Concat(s.Reverse());
+
+        var source = Enumerable.Range('0', '~' - '0').Select(x => (char)x);
+
+        var aggregateResult = source.Aggregate(string.Empty, Sum, Reverse);
+        var foldResult = source.Fold(string.Empty, Sum, Reverse);
+
+        Assert.That(aggregateResult, Is.EqualTo(foldResult));
+    }
+
+    [Test]
+    public void Fold_Throws_OnEmptyCollection()
+    {
+        Assert.Throws<InvalidOperationException>(() => Enumerable.Range(0, 0).Fold((x, y) => x + y));
+    }
+
+    private static void AssertMapBehavesSameAsSelect<TSource, TResult>(IEnumerable<TSource> source, Func<TSource, TResult> map)
+    {
+        var selectResult = source.Select(map);
+        var mapResult = source.Map(map);
+
+        Assert.That(selectResult.SequenceEqual(mapResult), Is.True);
+    }
+
+    private static void AssertFilerBehavesSameAsWhere<T>(IEnumerable<T> source, Func<T, bool> filter)
+    {
+        var whereResult = source.Where(filter);
+        var filterResult = source.Filter(filter);
+
+        Assert.That(whereResult.SequenceEqual(filterResult), Is.True);
+    }
+}

Functions/Functions.Tests/GlobalSuppressions.cs

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+// <copyright file="GlobalSuppressions.cs" company="Ilya Krivtsov">
+// Copyright (c) Ilya Krivtsov. All rights reserved.
+// </copyright>
+
+// This file is used by Code Analysis to maintain SuppressMessage
+// attributes that are applied to this project.
+// Project-level suppressions either have no target or are given
+// a specific target and scoped to a namespace, type, member, etc.
+using System.Diagnostics.CodeAnalysis;
+
+[assembly: SuppressMessage("StyleCop.CSharp.DocumentationRules", "SA1600:Elements should be documented", Justification = "This is tests project")]

Functions/Functions.sln

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+
+Microsoft Visual Studio Solution File, Format Version 12.00
+# Visual Studio Version 17
+VisualStudioVersion = 17.0.31903.59
+MinimumVisualStudioVersion = 10.0.40219.1
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Functions", "Functions\Functions.csproj", "{E71A4E78-9D6C-4616-9F99-3B067B9B92F3}"
+EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Functions.Tests", "Functions.Tests\Functions.Tests.csproj", "{D1AAD59B-65F4-4F94-B960-24C9DE9C1BB8}"
+EndProject
+Global
+	GlobalSection(SolutionConfigurationPlatforms) = preSolution
+		Debug|Any CPU = Debug|Any CPU
+		Release|Any CPU = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(SolutionProperties) = preSolution
+		HideSolutionNode = FALSE
+	EndGlobalSection
+	GlobalSection(ProjectConfigurationPlatforms) = postSolution
+		{E71A4E78-9D6C-4616-9F99-3B067B9B92F3}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{E71A4E78-9D6C-4616-9F99-3B067B9B92F3}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{E71A4E78-9D6C-4616-9F99-3B067B9B92F3}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{E71A4E78-9D6C-4616-9F99-3B067B9B92F3}.Release|Any CPU.Build.0 = Release|Any CPU
+		{D1AAD59B-65F4-4F94-B960-24C9DE9C1BB8}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{D1AAD59B-65F4-4F94-B960-24C9DE9C1BB8}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{D1AAD59B-65F4-4F94-B960-24C9DE9C1BB8}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{D1AAD59B-65F4-4F94-B960-24C9DE9C1BB8}.Release|Any CPU.Build.0 = Release|Any CPU
+	EndGlobalSection
+EndGlobal

Functions/Functions/Functions.cs

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+// <copyright file="Functions.cs" company="Ilya Krivtsov">
+// Copyright (c) Ilya Krivtsov. All rights reserved.
+// </copyright>
+
+namespace Functions;
+
+/// <summary>
+/// Utility class that contains Map, Filter and Fold functions.
+/// </summary>
+public static class Functions
+{
+    /// <summary>
+    /// Maps all elements from <paramref name="source"/> to elements of type <typeparamref name="TResult"/> using <paramref name="map"/> function.
+    /// </summary>
+    /// <typeparam name="TSource">Source type.</typeparam>
+    /// <typeparam name="TResult">Type to map to.</typeparam>
+    /// <param name="source">Source to map.</param>
+    /// <param name="map">Function that maps <typeparamref name="TSource"/> to <typeparamref name="TResult"/>.</param>
+    /// <returns>Sequence of mapped elements.</returns>
+    public static IEnumerable<TResult> Map<TSource, TResult>(this IEnumerable<TSource> source, Func<TSource, TResult> map)
+    {
+        foreach (var item in source)
+        {
+            yield return map(item);
+        }
+    }
+
+    /// <summary>
+    /// Filters elements from <paramref name="source"/> that satisfy <paramref name="predicate"/>.
+    /// </summary>
+    /// <typeparam name="T">Type of elements.</typeparam>
+    /// <param name="source">Source to filter.</param>
+    /// <param name="predicate">Function that filters elements; if it returns <see langword="true"/>, adds element to the result, otherwise, doesn't.</param>
+    /// <returns>Sequence of filtered elements.</returns>
+    public static IEnumerable<T> Filter<T>(this IEnumerable<T> source, Func<T, bool> predicate)
+    {
+        foreach (var item in source)
+        {
+            if (predicate(item))
+            {
+                yield return item;
+            }
+        }
+    }
+
+    /// <summary>
+    /// Folds all elements in <paramref name="source"/> into one element.
+    /// </summary>
+    /// <typeparam name="T">Type of elements.</typeparam>
+    /// <param name="source">Source to fold.</param>
+    /// <param name="folder">Function that is used to accumulate result.</param>
+    /// <returns>Accumulated value.</returns>
+    /// <exception cref="InvalidOperationException">Sequence is empty.</exception>
+    public static T Fold<T>(this IEnumerable<T> source, Func<T, T, T> folder)
+    {
+        var enumerator = source.GetEnumerator();
+
+        if (!enumerator.MoveNext())
+        {
+            throw new InvalidOperationException("No elements in source");
+        }
+
+        var value = enumerator.Current;
+
+        while (enumerator.MoveNext())
+        {
+            value = folder(value, enumerator.Current);
+        }
+
+        return value;
+    }
+
+    /// <summary>
+    /// Folds all elements in <paramref name="source"/> into one element.
+    /// </summary>
+    /// <typeparam name="TSource">Type of elements in <paramref name="source"/>.</typeparam>
+    /// <typeparam name="TResult">The type of accumulated value.</typeparam>
+    /// <param name="source">Source to fold.</param>
+    /// <param name="initialValue">Initial value of accumulated value.</param>
+    /// <param name="folder">Function that is used to accumulate result.</param>
+    /// <returns>Accumulated value.</returns>
+    public static TResult Fold<TSource, TResult>(this IEnumerable<TSource> source, TResult initialValue, Func<TResult, TSource, TResult> folder)
+    {
+        var value = initialValue;
+        foreach (var item in source)
+        {
+            value = folder(value, item);
+        }
+
+        return value;
+    }
+
+    /// <summary>
+    /// Folds all elements in <paramref name="source"/> into one element.
+    /// </summary>
+    /// <typeparam name="TSource">Type of elements in <paramref name="source"/>.</typeparam>
+    /// <typeparam name="TIntermediate">The type of accumulated value.</typeparam>
+    /// <typeparam name="TResult">The result type.</typeparam>
+    /// <param name="source">Source to fold.</param>
+    /// <param name="initialValue">Initial value of accumulated value.</param>
+    /// <param name="folder">Function that is used to accumulate result.</param>
+    /// <param name="map">Function that is used to convert accumulated result.</param>
+    /// <returns>Converted accumulated value.</returns>
+    public static TResult Fold<TSource, TIntermediate, TResult>(this IEnumerable<TSource> source, TIntermediate initialValue, Func<TIntermediate, TSource, TIntermediate> folder, Func<TIntermediate, TResult> map)
+    {
+        var value = initialValue;
+        foreach (var item in source)
+        {
+            value = folder(value, item);
+        }
+
+        return map(value);
+    }
+}

Functions/Functions/Functions.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Library</OutputType>
+    <TargetFramework>net9.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>